Journal of Physical Chemistry, Vol.99, No.35, 13272-13279, 1995
Velocity Distributions for a Laser-Vaporized, Anthracene-Labeled Nucleotide
We report the laser vaporization and multiphoton ionization of two anthracene-labeled molecules, N-(6-hydroxyhexyl)-3-(9-anthryl)propionamide and an anthracene-linked deoxythymine monophosphate. Laser vaporization of the anthracene-containing molecules was performed by directing, a high-intensity pulse (30-300 mJ/cm(2), 2.5 ns) of 532 nm laser light into a thin film of rhodamine 6G (Rh 6G) containing nanomolar quantities of the sample. Resonance-enhanced multiphoton ionization was used to selectively ionize the anthracene moiety in each molecule after vaporization. The S-0-S-1 transition of the anthracene molecule at 361 nm was used to excite the molecules, and ionization from this intermediate state was achieved using a 308 nm photon. The ionized products were detected and analyzed by mass spectrometry. The time-of-arrival measurements for the laser-vaporized molecules correspond to a bimodal velocity distribution, composed of a thermal component and a hyperthermal component showing substantial translational energy cooling. The distributions for the anthracene-labeled molecules reveal lower most probable velocities than those for the Rh 6G. A photochemical laser ejection model is proposed to-account for the energetic nonthermal velocity distributions measured.
Keywords:IONIZATION MASS-SPECTROMETRY;INDUCED THERMAL-DESORPTION;MATRIX;MOLECULES;SURFACES;FILMS;IONS;ABLATION;PROTEINS;MODEL